Synthetic Inorganic Chemistry

ELEMENTS AND WATER 69

is evolved freely which burns with a colorless flame character-

istic of hydrogen. The contents of this tube grow very hot,

and the amalgam disintegrates to yield a finely divided gray

powder which stays suspended in the water.

In experiment (b) the action was extremely slow until the
magnesium reached its melting point. From then on no coherent
film would stick to the liquid surface, and without this mechanical
hindrance to the reacting substances coming in contact with each
other, the natural activity of the magnesium came into play.
In experiment (c) the amalgam is liquid or at least semi liquid
so that no coherent film of magnesium hydroxide can adhere to the
surface.
That magnesium must be a much more active element than hy-
drogen is shown by the vigor with which it displaces it; in ex-
periment (6), for example, the fact that the oxygen with which the
magnesium was combining had to be withdrawn from its com-
bination with hydrogen did not appear to diminish the vigor of the
reaction sensibly, for the incandescence seemed as bright as if the
magnesium ribbon had been burning in oxygen.

8. Iron and Water. Iron filings do not produce any
   measurable quantity of hydrogen either in cold or hot water.
   Set up the apparatus described in Experiment 7 (b). Put a
   layer of fine iron filings in the middle of the combustion tube
   in place of the magnesium. Heat cautiously to vaporize the
   liquid water condensed in the tube, and then heat the iron
   filings strongly. As the steam from the delivery tube con-
   denses in the water in the trough it is seen that an occasional
   bubble of gas rises in the test tube. After a short time enough
   has collected to test and it is found to bum like hydrogen.

Apparently in this case the coating of oxide on the surface

of the iron is not entirely impervious to gases. At the high tem-

perature the steam diffuses more rapidly through the layer and

thus the production of hydrogen becomes measurably rapid.

9. Removal of Protective Coating by Chemical Action.
   Note that aluminum metal resembles magnesium in that it
   displays a brilliant metallic luster when its surface has just
   been scraped but it quickly loses the brightness of its luster.